Offshore platforms are expensive to manufacture. Often they have to be developed with a particular region and water depth in mind. In addition, the platforms are often large and difficult to transport or construct. Thus, there is a great need for more efficient designs and methods of construction. Certain prior art platforms employ stackable modules in the support structure for the platform. Wetmore, U.S. Pat. No. 4,511,288, for example, discloses stackable modules, however these modules are heavy, walled, and dense structures, weighing thousands of pounds, and they are not interchangeable. Moreover, the modules in Wetmore do not make up a jacket assembly. A jacket assembly, as the term is used in this patent means a skeletal structure, designed for supporting an offshore platform, which is comprised of a plurality of rigid members which are joined together.
Horton, U.S. Pat. No. 4,492,270 discloses a well jacket assembly with standardized nodes and cross members but does not disclose stackable, interchangeable modules. Turner et al., U.S. Pat. No. 4,958,960 discloses a "modular" structure however there is no indication that the "module" is constructed with stackable interchangeable modules. In addition the "modular" structure is structurally separate from the jacket assembly.
In the prior art a support structure frequently used for the platform was a jacket assembly, consisting of six substantially vertical legs, as in the case of Turner et al., U.S. Pat. No. 4,958,960. The horizontal cross section of such a jacket assembly is rectangularly shaped. Armstong, U.S. Pat. No. 4,161,376, however, discloses a triangular cross section in which only three legs are used, and Horton U.S. Pat. No. 4,492,270 discloses the use of three jackup legs (see FIG. 1).
In the prior art, conductors for transporting fluid were usually structurally separate from the supporting elements of the platform. Armstong, U.S. Pat. No. 4,161,376 discloses that leg 12 can be provided with conductors to allow anchoring and drilling therethrough. However, Armstong is not directed to a modular construction for a jacket assembly. McGehee U.S. Pat. No. 4,813,815 discloses that fluid can be transported through a joint, however, McGehee is not directed to a jacket assembly but rather a single rotatable bouyant column.
In the prior art, jacket assemblies were constructed so that at least some of the jacket assembly was above the water surface. See Wetmore, U.S. Pat. No. 4,511,288, FIG. 1; Horton, U.S. Pat. No. 4,492,270, FIG. 1; Armstong, U.S. Pat. No. 4,161,376, FIG. 7; although McGehee U.S. Pat. No. 4,813,815 states that the platform can be in or above the water, it is directed toward a buoyant rotable column, and not a jacket assembly as noted above.